The present invention relates to a plasma processing apparatus and a plasma processing method and, particularly, to a plasma processing apparatus and a plasma processing method in which surface processing of a semiconductor substrate or the like is performed while gases are periodically switched during plasma processing.
Due to miniaturization in a recent semiconductor technology, higher shape controllability is demanded for etching processing in which a mask shape is transferred onto an underlying film. Various etching methods of a vertical shape having a high aspect ratio are known, and among them, there is known a gas chopping method, in which an etching gas and a deposition gas that forms a protective film having high etching resistance against the etching gas are alternately introduced into a processing chamber in a cyclic manner while a plasma is kept being generated so that plasma etching processing is performed as a whole.
For example, JP-A-S60-050923 discloses a technology in which radio frequency (RF) power supplied to a sample stage is also changed in synchronization with gas introduction to generate different self-biases in a process of introducing the etching gas and a process of introducing the deposition gas for the purpose of enhancing effects of the respective gases when the gases are alternately introduced.
When etching processing is performed while alternately performing the etching and the protective film formation using the gas chopping method, an unpreferable shape of fine steps called “scalloping” is formed on aside surface of an etched hole after etching. In order to mitigate the fine-step shape, it is effective that respective times of introduction of the alternately-introduced gases are shortened down to 1 to 3 seconds.
Control of an amount of gas introduced into the processing chamber is typically conducted by providing a control signal to a mass flow controller (MFC) which makes the gas flow at a desired gas flow rate. However, a delay of about 1 second occurs until the gas is introduced into the processing chamber after the signal of a flow rate is provided to the mass flow controller due to the influences of a response time of the mass flow controller, gas piping or a shower plate, a pressure and a gas flow in the processing chamber, and the like; in addition, the delay varies by about 0.2 to 0.3 seconds.
Therefore, when the introduction time period of a gas is set to about 1 to 3 seconds, deviations in time between a duration when a process gas for etching or protective film formation is introduced in the processing chamber and a duration when process parameters such as a bias and power for generating plasma are controlled to values suitable for respective processings become innegligible and optimized processings can not be realized if control is not performed in consideration of the delay from providing a control signal to a mass flow controller until the gas is actually introduced into the processing chamber.
Furthermore, in order to reduce influences of variations in the delay time of the gas introduction, other process parameters may necessarily be controlled while monitoring an exact time of the gas introduction into the processing chamber in real time. As a method of determining exchange of the etching gas and the deposition gas, a method such as that disclosed in JP-A-H02-105413 is known, in which the timing point of replacement of the etching gas and the deposition gas is obtained by detecting a gas ratio using an emission spectrum or a mass spectrometer and radio frequency power is synchronized with it.